Various dispensing systems have been used in the past for applying patterns of viscous material onto a moving substrate. In the production of disposable diapers, incontinence pads and similar articles, for example, hot melt adhesive dispensing systems have been developed for applying a laminating or bonding layer of hot melt thermoplastic adhesive between a non-woven fibrous layer and a thin polyethylene backsheet. Typically, the hot melt adhesive dispensing system is mounted above a moving polyethylene backsheet layer and applies a uniform pattern of hot melt adhesive material across the width of the backsheet substrate. Downstream from the dispensing system, a non-woven layer is laminated to the polyethylene layer through a pressure nip and then further processed into a final product.
In one known hot melt adhesive dispensing system, continuous beads or filaments of adhesive are emitted from a multiple adhesive outlet die with multiple air jets oriented around the circumference of each material outlet. The multiple air jets are tangentially directed relative to the orientation of the adhesive filament as it emits from the die orifice, thereby attenuating each adhesive filament and causing the filaments to swirl before being deposited on the upper surface of the moving substrate.
More recently, manufacturers of diaper products and others have been interested in small fiber technology for the bonding layer of hot melt adhesive in non-woven and polyethylene sheet laminates. To this end, hot melt adhesive dispensing systems have incorporated slot nozzle dies with a pair of angled air channels formed on either side of the elongated extrusion slot of the die. As the hot melt adhesive emits from the extrusion slot as a continuous sheet or curtain, pressurized air is emitted as a pair of curtains from the air channels to impinge upon, attenuate and fiberize the adhesive curtain to form a uniform fibrous web of adhesive on the substrate. Recently, fibrous web adhesive dispensers have incorporated intermittent control of adhesive and air flows to form discrete patterns of fibrous adhesive layers with well defined cut-on and cut-off edges and well defined side edges.
Meltblown technology has also been adapted for use in this area to produce a hot melt adhesive bonding layer having fibers of relatively small diameter. Meltblown dies typically include a series of closely spaced orifices in one or more dies or nozzles that are aligned on a common axis across the die head. An angled air channel is provided on each side of the orifices. As hot melt adhesive emits from the series of aligned nozzles, pressurized air is emitted from the air channels as a pair of curtains that impinge upon, draw down and attenuate the fibers before they are applied to the moving substrate.
While these prior systems have been used to produce fibrous adhesive layers on moving substrates, it is still desired to continue to improve the controllability of the dispensed liquid material patterns, in particular, the frequency of oscillation of the dispensed liquid material.